1. Field of the Invention
The present invention relates to a control device for positioning a head in a target position, a disk device, and a seek orbit generation method, and more particularly to a control device which performs seek control by supplying a two-degree-of-freedom control system with a target position orbit, a disk device, and a generation method for generating the target position orbit.
2. Description of the Related Art
With a disk device for a disk such as an optical disk or magnetic disk, it is extremely important to position the head in a target position accurately. An example of such positioning control is seek control.
A positioning control system having a driving unit which moves a controlled body, and a calculation control unit which controls the driving unit has been disclosed as an example of the related art of seek control. In this system, a target position, a target velocity, and a target acceleration are expressed respectively by time-related, fixed polynomials, and the driving unit is controlled by having the calculation control unit calculate the target position and so on at regular sample time intervals (for example, Japanese Patent No. 2657561 and Japanese Patent No. 2736715).
A method of performing seek control while estimating a head velocity using an observer by supplying a two-degree-of-freedom control system with the head velocity has also been disclosed (for example, “DSP Technology in a Hard Disk Drive”, Eiji Okamura, Electronics, November 1996, p 38-45).
However, in the prior art described above, there is no description of seek control performed by supplying a two-degree-of-freedom control system with a target position orbit. In particular, there is no description of a method of generating a target position orbit in real time.
Meanwhile, in a two-degree-of-freedom control system, a filter may be constituted by an inverse function of a transfer function constituting a feedback loop to realize an ideal control circuit in which the relationship between a target position orbit r and an observation position y is y/r=1. However, when the filter is thus constituted, high frequency noise is amplified infinitely, and hence realization is impossible.
Also in a two-degree-of-freedom control system, a transfer function from the target position orbit to the observation position may be approximated by a second-order low-pass filter (LPF). However, when the target position orbit is varied in stepped form, the current of the driving unit for driving the head may not be symmetrical between the acceleration area and deceleration area, depending on the constitution of a second-order LPF, and hence seek control takes a great deal of time.